Saw cut joint
A control joint created by sawing a groove into hardened concrete. Timing is critical: too early and the edges ravel, too late and the slab has already cracked.
What does saw cut joint mean?
Conventional wet or dry sawing waits until the concrete is hard enough not to tear, which on a hot day can be a matter of hours after final set. The cut must reach a depth that reliably creates a weak plane through the slab thickness. Sawing generates respirable silica dust, so water feed or vacuum dust collection is a regulatory requirement, not an option.
In practice
A saw crew arriving the next morning instead of the same evening is the most common reason a slab cracks outside its joints.